The tension around the ass when holding in a fart for a protracted period of time.

when you have to fart but for some reason you cant let loose ie you're stuck in an elevator, in bed with someone you DONT fart around etc

example- i was stuck on the elevator when i realized the steak'ncheese for lunch was about to blow my ass out, but the hot chick from down the hall was on the elevator so i had to hold it for 17 floors before i could hop out and let loose...if i had waited to get out any longer my fartstranglitis would have brought me to my knees in pain.